DESCRIPTION (Investigator's Abstract): Microtubules and microtubule-associated proteins (MAPs) are filamentous ultrastructural components that are essential for axon and dendrite formation. One function of microtubules is to transport axon "building materials" between the cell soma and the axon. Microtubules associated proteins 1A and 1B, the MAP1 proteins, are structurally related proteins with binding sites for microtubules, microfilaments, and common polypeptide subunits. The MAP 1 proteins are the most abundant microtubule-associated proteins in axons, yet their function remains unknown. MAP1 proteins are widely speculated to interact with microtubules to establish, organize, and maintain the structure of the axonal cytoskeleton. Our broad objective is to test this hypothesis by determining the ultrastructural consequences of changing MAP1 concentration and by manipulating specific intra- and intermolecular interactions of MAP 1 protein. A thorough understanding of MAP1 molecular interactions will provide the foundation for manipulating MAP1 activity to optimize nervous system regeneration and to identify and prevent any specific diseases caused by altered MAP1 activity. This project has five aims: 1) To characterize a MAP1 protease activity that dramatically alters the structure of MAP1 proteins. The MAP1 protease recognition sequence will be identified. The intramolecular interactions required for MAP1 polyprotein proteolysis will be defined. This information will be used in future studies to develop MAP1 protease inhibitors, to determine the consequences of protease inhibition on neuron function, and to purify the MAP1 protease. 2) To identify MAP1 subunit interactions that are essential for microtubule binding activity. This information is needed to establish a mechanism by which MAP1 proteins organize and strengthen the axonal cytoskeleton. 3) to determine the primary amino acid sequence of a 70 kDa protein associated with the MAP1 proteins. This molecule is a candidate for the MAP1 protease. 4) to measure the effects of decreasing and increasing MAP1B on microtubule organization and the ability of neurons to extend axons. 5) To measure the effect of deleting MAP1B on the organization of the neuronal cytoskeleton in a transgenic mouse. The last two aims directly test the role of MAP1 proteins in establishing, organizing and maintaining the axonal cytoskeleton.